In many circumstances it is important to measure the temperature inside a material body. Such circumstances may occur during industrial processes or exploration and analysis processes, such as in geophysical probing or in medical diagnostics and treatment of internal parts of the body.
Conventional thermometry and absolute thermometry are known methods for measuring temperature.
Conventional thermometry is based upon the temperature coefficient of properties of materials, such as resistance or mechanical expansion.
Absolute thermometry is a method which directly measures thermal energy of a sensor resistance. This method is based upon the known physical phenomenon of spontaneous thermal noise arising from the Brownian motion of ionized molecules within a resistance.
Thermal noise, which can be discussed in terms of thermal current, provides a direct measurement of temperature on a thermodynamic scale, thus the Boltzmann constant defines the temperature. The phenomenon of thermal noise is derived, for example, in the book: CCD arrays cameras and displays by Holst G. C., p. 128, 2nd edition, SPIE Press, 1998. A formula that may be used to define thermal current is, for example:<in2>=k T Cwhere k is the Boltzmann constant, T is the temperature of a sensor, and C is the capacitance of the sensor. Thus the magnitude of the signals produced by the thermal current is directly proportional to the square root of the temperature of the sensor. Experiments have indicated that the signal doubles with the increase of 7° C. (degrees Centigrade), which means that a resolution better than 0.1° C. is achieved.
In image sensors, the thermal current produced in an operating photodetector device, when no optical radiation impinges on the detector, is called “dark current”. In CCD cameras dark current is basically charge which accumulates in the CCD pixels due to thermal noise. The effect of dark current is to produce an additive quantity to the electron count in each pixel.
U.S. Pat. No. 3,937,086 to von Thuna, U.S. Pat. No. 5,354,130 to Seppa et al. and U.S. Pat. No. 5,098,197 to Shepard et al. all describe devices for measuring the absolute temperature of a body material by receiving and analyzing the thermal noise of the body material.
U.S. Pat. No. 4,246,784 to Bowen describes a method for noninvasive temperature measurement of th interior of a body using the acoustic thermal noise spectrum of the measured body.
None of these temperature measurement methods utilize an image sensor to measure the thermal noise of a body material.